Conventional tube benders of the type under consideration include first and second spaced back gates receiving back shoes. Each of these back shoes comprises a block having a cylindrical cut-out on one side of given axial length for engaging a side wall portion of one side of a tube to be bent. A radiused ram in turn is positioned to engage against an opposite central side wall of the tube when urged along an axis passing between the back gates and back shoes. The back gates and shoes supported thereon are swingable in opposite directions as the ram die moves along the axis between the back gates to thereby form a bend in the tube.
When tubes of different diameter are to be bent, it is necessary to change the back shoes to provide shoes with cylindrical cut-outs conforming to the cylindrical outside diameter of the tube in question. The axial length of the cut-out in each shoe may vary depending upon the diameter of the tube and normally there is an optimum relationship for effecting proper yielding during the bending operation of the material of the tube to form a proper bend.
In certain types of tube bending operations such as in forming exhaust pipes for automobiles, first and second bends in the tube must oftentimes be made relatively close together. With the conventional back shoes, the axial length of the cylindrical cut-out engaging side portions of the tube is such that a second bend cannot be made as close to a first bend as required. The reason is that the length of the shoe is such as to interfere with the first bend in initially positioning the pipe for the second bend. In other words, there must be a certain amount of spacing between the first and second bend in order that the shoes can properly engage the tube side walls to form the second bend.
Under the foregoing circumstances, an operator must remove one of the standard conventional shoes and insert one having the same cylindrical cut-out diameter but of shorter axial length so that the second bend can be made correspondingly closer to the first bend without interference with the shoe. After such second bend is made, and normal bending operations are to resume, the operator will remove the shorter shoe and insert a conventional shoe for the remaining bends which are normally spaced a sufficient distance apart that the conventional shoes can be used.